A fuel cell generally includes a stack of power generating elements which process reactants such as hydrogen and oxygen in an electro-chemical reaction which produces electrical energy. The reaction is exothermic, generating heat as well as by-product water. The heat of reaction must be continuously removed in order to prevent the cell temperature from rising above the optimum temperature for system efficiency.
Burst power fuel cells are devices which release substantial amounts of energy in very short time periods, on the order of seconds to minutes, in contrast to the much longer periods provided by non-burst power fuel cell systems. Such a rapid release in energy requires a complimentary rapid heat absorbing system in order to maintain the cell at its optimum operating temperature during the discharge cycle. Such burst power fuel cells have particular application in a number of emerging space missions which will require space based, electrically powered devices capable of providing instantaneous power bursts. Such a utilization places special limitations in terms of weight and complexity on the choice of a cooling system.
In U.S. Pat. No. 3,253,423, a cryogenic cooling system for space vehicles is disclosed which utilizes solid hydrogen as a cooling agent. Besides the hazards and complexity involved in loading such a system, there is a particular problem with venting the apparatus to space, with such venting causing platform instabilities. In addition, such vented gases can detrimentally affect platform sensors and impair or interrupt any beams or signals the device may be emitting or receiving from ground based or spaced based sources. The use of a radiator to cool the system, shown in FIG. 1 of the above-referenced patent, results in a system which is vulnerable to damage by meteroids or other debris. In addition, such a radiator is quite heavy, comprising a significant portion of the system weight and thereby adding a substantial fuel penalty on launch.
In U.S. Pat. No. 3,466,199, an isothermal assembly is disclosed for insulating a device from extreme cold by encasing it in ice. This provides a constant 0.degree. C. temperature to the insulated device. While useful in insulating a passive device from extremely cold temperatures, it would not provide temperature control of an active heat generating device.
Generally, ground based fuel cells utilize double-loop cooling systems which require pumps, heat exchangers and complex piping (see FIG. 1). While providing safe and efficient cooling for ground base fuel cells, limitations in terms of weight and space preclude the adaptation of such cumbersome systems to space based fuel cells. Consequently, what is needed in the art is a cooling system adaptable to space based burst power fuel cells which conforms to the severe restrictions in terms of weight, space and emissions.